There are several approaches used in the electronic industry today that address how to solder attach a contact such as a pin to a PCB or other substrate (e.g., FR-4, ceramic, plastic, Teflon, metal etc.) using a solder paste and reflow process. These approaches include:                1. Interference Fit Pin Through Paste: This scheme uses a pin with an interference fit, such as when the pin is square and interferes with a round hole or has a protrusion/interference section along the shank of a round or square pin. The square pin or the interference section provides an interference fit when inserted into a hole of a PCB. Pre-deposited solder paste in or around the hole that the pin is inserted into provides a preferred solder joint when reflowed as would a secondary wave solder process. A problem with this approach is that it requires specialized insertion equipment and component packaging and processing. Also, pin interference can cause damage to the pins.        2. Surface Mount in Paste: In a conventional purely “top side”, non-through hole application, solder paste is applied to a surface mount pad and a pin is placed onto the pad. The pin typically has a larger “foot” geometry, which is used to maximize the surface area for a preferred solder joint and stabilize the pin during the reflow process. The same problem with this approach exists, namely, it requires specialized equipment and packaging, and provides a single-sided pin interconnect only.        3. Compliant Pins: In this application, no solder is required and a spring-like interference fit is used to make contact to a plated through-hole in the PCB. Again, this approach requires specialized equipment and packaging.        4. Paste After Pin: In this scheme, an interference-fitted pin is inserted flush into the substrate, next the substrate is flipped or inverted, and then solder paste is deposited over the pin hole and reflowed. Again, this approach requires specialized equipment and packaging.        
These standard approaches will not satisfy the requirements for a reliable soldered pin interconnect where very thin boards are used, or where an intrusive interference lit or second-sided surface mount processing can not be used. Second-sided surface mount processing means that the second side of the board is processed after the first side of the board has been processed to mount components or board interconnects or make connections.
Also, softer materials such as Teflon can not withstand the forces needed with interference pins to retain the pin into the plated through-hole of the bare board accurately. Still further, there are times when board hole diameter tolerances cannot be held tight enough for an interference fit with smaller pins. Also, the surface mount pin approaches require secondary processing when a pin interconnect is required from the second side of the board.